Twisted Trees

[an error occurred while processing this directive]

The walking tree islands provide homes for animals and stability
for us

Shaped by wind, ice, and cold, the trees of the alpine tundra evolve
into an array of forms called krummholz, a German word that means
"twisted wood." Found in the transition zone between the forest
and treeless tundra in alpine and Arctic areas, krummholz varies
depending on latitude and altitude. In the far north, it stretches
in a swath, often hundreds of miles wide, across North America,
Siberia, the Europe. In the Appalachians of the eastern United States,
krummholz is found right at rimberline, spread only a few feet across.
The reason: Weather conditions, even at high elevations, aren't
harsh enough to force a transition from forest to tundra. In the
West, krummholz is extremely common in the higher Rockies and the
Pacific coastal mountains.

[an error occurred while processing this directive]

At the edge of the timberline, trees are thrashed and ice-blasted.
Such trees may brow only inches high, rivaling even the most assiduous
pruning of a bonsai expert. But krummholz can also send out ground-hugging
branches great distances, sometimes forming a sprawling cushion
that can be as much as 50 feet in diameter. These stunted trees
often huddle together for protection in tree islands that stand
alone amid the wide-open meadows of the treeless tundra.

The close clumping of vegetation in krummholz tree islands protects
more than the trees themselves. For animals such as voles that frequent
tundra meadows, the islands provide quick cover from predators.
For birds such as white-crowned sparrows, they offer cozy spots
for nesting in an environment that otherwise provides scant shelter.
For wintering animals such as gophers, tree islands give shelter
from howling winds. And for us, krummholz provides some stability:

The tenacious vegetation helps fasten snow and rock on steep mountain
slopes, reducing the risk of avalanches and landslides. Krummholz
is also important for scientists monitoring the effects of global
warming. Several studies have already shown a shift from krummholz
to ordinary forest coinciding with warming temperatures. For example,
researchers at Laval University in Sante-Foy, Quebec, have found
that since the late 1800's, the forest line has moved more than
two and a half miles north, most likely in response to milder winters.

Condos, towns, and other high-country outposts of civilization
in North America might also be toast if it weren't for krummholz.
On this continent, timberline and krummholz are intact. Their root
systems are doing what isn't being done in Europe: stabilizing snow
and fragmented rock. Timberline trees in Europe still have not recovered
from grazing and woodcutting in medieval times. As a result, snow,
soil, and rock on steep slopes are more apt to slide. They've been
denuded, with disastrous effects.

As we head up the ridge, the spruce and fir become increasingly
stunted and wind-sculpted. Higher still, we emerge into the realm
of the mobile tree islands. Scattered across the tundra, some are
as small as a Volkswagen Bug, others as big as a bus. At the windward
side of these clusters, the trees attain a height of no more than
six inches or so. Toward the back, the trees rise and the island
widens. At the very rear, the trees are about chest high. In profile,
the grove looks strangely like the front of a bullet train.

At the front, facing toward the winde, there's considerable dieback
of vegetation, where the island is eroding away. It seems abundantly
clear how an island of trees like this can migrate downwind, away
from the nasty assault of wind and cold.

The soil in the "wake" of an island loses about 25 percent of the
carbon it once contained. Tundra soils contain among the highest
concentrations of carbon in thw world. If global warming were to
cause trees to enroach on the tundra, a substantial amount of that
carbon would be lost from the soil. Part of the carbon would likely
wind up in decayed plant material on the ground's surface. The rest
would be incorporated into the tissues of the new trees growing
on former tundra.